The present invention relates generally to a light coupling assembly for use with medical instruments. More particularly, it relates to a light coupling assembly and associated system specifically configured to receive light from a remote source of light, which also generates heat, and to then direct this light to an instrument such as, for example, an endoscope such as a laryngoscope, through a fiber-optic cable in a way which prevents heat generated by the light source from damaging the fiber-optic cable.
Systems including a light source and associated equipment for coupling light from a light source to a medical instrument are known in the art. Typically, such systems utilize glass fiber-optic cable to couple the source light to the instrument and, thereafter, illuminate a particular area of a patient's anatomy. A medical practitioner can then view the illuminated area during a particular procedure by using a viewing arrangement such as a fiber-optic cable with an attached eyepiece. Such a prior art viewing arrangement is shown in U.S. Pat. No. 4,337,761, issued to the inventor of the present invention, in association with a laryngoscope so that an image of the illuminated area is provided at the eyepiece. In using such past systems, however, the subject anatomical area is generally rather dimly illuminated because relatively weak light sources are used, as these sources are typically powered by batteries housed, for example, in the handle of the instrument. More recently, external light sources have been provided. These sources typically couple light from a remote light source directly into a glass fiber-optic cable. However, illumination levels have not been dramatically improved by such external light sources. The relatively low light levels have been acceptable only because they are compensated for by the relatively sensitive eye of the practitioner directly viewing the image at the eyepiece.
Recent advances in the field of video imagery, including the availability of compact low cost CCD video cameras, have resulted in a fundamental change in the way practitioners may perform such procedures. It is now highly possible to directly couple a video camera to an eyepiece or other such arrangement whereby to allow a practitioner to view a procedure on a video monitor. This technique is advantageous for a number of reasons. For one, such a system is extremely useful in an instructional environment for training new practitioners. Trainees may be present for observation as the procedure is being performed or, alternatively, the procedure may be recorded for later viewing in a classroom environment. Additionally, a permanent video record of the procedure may prove to be useful for insurance and other purposes.
Unfortunately, the use of even the latest video camera requires relatively bright illumination of the patient's anatomy. It would seem that the simple expedient of increasing the brightness of the light source in the above described external source would resolve this problem. However, the light source also generates heat and a significantly brighter light source, which is suitable for use with a video camera, produces much more heat than former light sources which were used in conjunction with direct viewing by the human eye. In fact, the heat produced is increased to a level at which direct exposure damages plastic fiber-optic cables of this type which are desirable for use in this application. In prior art systems utilizing external light sources, such cables are positioned in close proximity with the light source to initially receive light for transmission to the instrument. This type of arrangement is not suitable for use with light sources contemplated for use with state of the art video viewing arrangements since the plastic fiber optic cable will ultimately be damaged by the generated heat of the light source. Substitution of other heat resistant light conductive materials such as, for example, glass or quartz in place of the plastic fiber-optic cable is also problematic. These alternate materials, while being less sensitive to heat, are also characterized by high internal light transmission losses. In addition, they are extremely expensive and have a tendency to break due to their multiple tiny fiber construction. Therefore, the use of these alternate materials, as a direct substitute for plastic fiber-optic cable, is self-defeating in that transmission losses are high enough that it becomes difficult to achieve acceptable illumination levels, without using very large composite bundles, and even when using the much brighter light sources contemplated by the present invention. It should be added that composite bundles have dead space between the fibers which significantly decrease their functional cross-section. This is not true of solid plastic fibers.
The present invention resolves the foregoing difficulties by providing a highly advantageous light coupling assembly which is adapted for use with an intense, heat producing light source and which couples this intense light to a low loss fiber-optic cable in a hybrid light path without subjecting the latter to damaging levels of heat produced by the light source; the cable can be made of a heat sensitive material, such as plastic, rendering the cable both light weight and disposable.